Phosphor converted light emitting diode, a lamp and a luminaire

ABSTRACT

A phosphor converted Light Emitting Diode (LED), a lamp and a luminaire are provided. The phosphor converted LED comprises a LED, a first luminescent material, a second luminescent material and a third luminescent material. The LED emits a first spectral distribution having a first peak wavelength in the blue spectral range. The first luminescent material absorbs a portion of the light of the first spectral distribution and converts at least a portion of the absorbed light towards light of a second spectral distribution. The second spectral distribution has a second peak wavelength in the green spectral range. The second luminescent material absorbs absorbing a portion of the light of the first spectral distribution and/or a portion of the second spectral distribution. The second luminescent material converts at least a portion of the absorbed light towards lights of a third spectral distribution. The third spectral distribution has a third spectral width and has a third peak wavelength. The third luminescent material absorbs a portion of the light of at least one of the first spectral distribution, second spectral distribution, and the third spectral distribution. The third luminescent material converts at least a portion of the absorbed light towards light of a fourth spectral distribution. The fourth spectral distribution has a fourth spectral width and has a fourth peak wavelength. The third peak wavelength and the fourth peak wavelength are in the orange/red spectral range. The third peak wavelength is smaller than the fourth peak wavelength and the third spectral width is larger than the fourth spectral width.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 14/419,951 filed on Feb. 6, 2015, titled “PHOSPHOR CONVERTED LIGHTEMITTING DIODE, A LAMP AND A LUMINAIRE”, which is a §371 application ofInternational Application No. PCT/IB2013/056441 filed on Aug. 6, 2013,which claims priority to U.S. Provisional Patent Application No.61/681,695 filed on Aug. 10, 2012. U.S. patent application Ser. No.14/419,951, International Application No. PCT/IB2013/056441, and U.S.Provisional Patent Application No. 61/681,695 are incorporated herein.

FIELD OF THE INVENTION

The invention relates to phosphor converted Light Emitting Diodes havinga relatively large Color Rendering Index. The invention further relatedto the use of the phosphor converted Light Emitting Diodes in lamps andluminaires.

BACKGROUND OF THE INVENTION

Phosphor converted Light Emitting Diodes (LEDs) comprise luminescentmaterials such as inorganic phosphors to convert a portion of the lightemitted by the LED into light of another color to obtain a specificlight emission. Many phosphor converted LEDs are used to obtain anemission of light with a color point close to the black body line in acolor space—hence, light which appears to be white to the human nakedeye. The phosphor material is often applied directly on the LightEmitting Diode, however, the invention disclosed in this document is notdirectly limited to such embodiments.

Currently, the above discussed phosphor converted LEDs are based on bluelight emitting LEDs which are combined with luminescent materials whichconvert a portion of the blue light to green and to red light togenerated white light which has a relatively high color rendering index,for example, larger than 80. One example of such phosphor converted LEDsis a LED which emits blue light with a peak wavelength of 449 nanometer,which comprises a green emitting phosphor Y₃AL₅O₁₂:CE³⁺ and a redemitting phosphor CaAlSiN₃:Eu²⁺. The red emitting phosphor emits redlight according to a spectral distribution which has a peak wavelengthat 620 nanometer and a width of 93 nanometer (expressed as a Full WidthHalf Maximum, FWHM, value). By combining specific amounts of thephosphors, a phosphor converted LED may be manufactured which emitslight at the correlated color temperature CCT=3000 Kelvin. The totallight emission power of this specific phosphor converted LED comprisesabout 11% light from the blue emitting LED, 43% light from the redemitting phosphor and about 46% light from the green emitting phosphor.The total lumen equivalent is 322.2 lumen per Watt and the Color RendingIndex (expressed as an RA value) is 82.1.

The lumen equivalent strongly depends on the amount of light that thered emitting phosphor emits in the deep red region. The deep redspectral range starts at about 650 nanometer, with the eye sensitivitydropping below 10 percent of its maximum. If the amount of light emittedin the deep red region can be limited, the lumen equivalent ispotentially higher.

In order to improve the lumen equivalent, it is know that Quantum Dots(QDs) can be used because quantum dots have a relatively narrow lightemission spectrum. There are, for example, QDs which emit light with apeak wavelength in the range from 610 to 620 nanometer and have a lightemission spectrum which has a width of 30 nanometer FWHM. For example,when a phosphor converted LED is manufactured, which comprises a blueemitting LED which emits a peak wavelength of 449 nanometer, whichcomprises a green phosphor Y₃Al₅O₁₂:Ce³⁺, which comprises red emittingquantum dots with have a emission spectrum with a peak emission of 612nanometer and a width of 30 nanometer FWHM and which is configured toemit light at the CCT of 3000 Kelvin, the emitted light has the samecolor rendering index as the phosphor converted LED of the previousparagraph (CRIRA=82.1), and the lumen equivalent increased towards 364.9lumen per Watt. Thus, if two phosphor converted LEDs in accordance withthe previous two embodiments are provided with the same amount ofelectrical energy, the human naked eye experiences the emitted light bythe last phosphor converted LEDS as more bright light.

However, the quantum dot material is not yet reliable enough toguarantee a long life time of the phosphor converted LED. Further, themost efficient quantum dot materials today available comprise Cadmiumand/or Selenide which have known environmental compatibility issues.Furthermore, known alternative luminescent materials which emit redlight at a relatively high peak wavelength and which emit light in anarrow band have also stability problems.

SUMMARY OF THE INVENTION

It is an object of the invention to provide phosphor converted LightEmitting Diodes (LEDs) which are more stable than the know phosphorconverted LEDs while maintaining a relatively high lumen equivalent anda relatively high color rendering index.

A first aspect of the invention provides a phosphor converted LightEmitting Diode. A second aspect of the invention provides a lamp. Athird aspect of the invention provides a luminaire. Advantageousembodiments are defined in the dependent claims.

A phosphor converted Light Emitting diode (LED in accordance with thefirst aspect of the invention comprises a LED, a first luminescentmaterial, a second luminescent material and a third luminescentmaterial. The LED emits a first spectral distribution having a firstpeak wavelength in the blue spectral range from 445 nanometer to 495nanometer. The first luminescent material absorbs a portion of the lightof the first spectral distribution and converts at least a portion ofthe absorbed light towards light of a second spectral distribution. Thesecond spectral distribution has a second peak wavelength in the greenspectral range. The second luminescent material absorbs absorbing aportion of the light of the first spectral distribution and/or a portionof the second spectral distribution. The second luminescent materialconverts at least a portion of the absorbed light towards lights of athird spectral distribution. The third spectral distribution has a thirdspectral width and has a third peak wavelength. The third luminescentmaterial absorbs a portion of the light of at least one of the firstspectral distribution, second spectral distribution, and the thirdspectral distribution. The third luminescent material converts at leasta portion of the absorbed light towards light of a fourth spectraldistribution. The fourth spectral distribution has a fourth spectralwidth and has a fourth peak wavelength. The third peak wavelength andthe fourth peak wavelength are in the orange/red spectral range. Thethird peak wavelength is smaller than the fourth peak wavelength and thethird spectral width is larger than the fourth spectral width.

The phosphor converted LED according to the first aspect comprises twodifferent luminescent materials which convert blue light towardsorange/red and red light. The third luminescent material, comprisingquantum dots for example, has the highest peak wavelength and, thus,emits light which is close to the deep red spectral range. The spectraldistribution of the third luminescent material has a relatively narrowlight emission distribution, especially compared to the secondluminescent material. Thus, the third luminescent material does not emitmuch light in the deep red spectral range, and, thus, the lumenequivalent is not reduced because of a too large light emission in thedeep red spectral range. The second luminescent material has a lowerpeak wavelength in the orange/red or red spectral range and has a widerlight emission distribution (compared to the third luminescent material)and, consequently, the second luminescent material emits light in thelower red spectral range and partly in the spectral range in which thethird luminescent material also emits light. Thus, the secondluminescent material contributes to a high enough light emission alongthe whole red spectral range and possibly also in the orange spectralrange. Thereby, the color rendering index of the light emitted by thephosphor converted LED remains relatively high. Furthermore, by using asecond luminescent material which emits also some light in the spectraldistribution of the third luminescent material, the required amount ofthe third luminescent material may be reduced which is especiallyadvantageous if the third luminescent material is expensive or hasspecific disadvantages. If the amount of the third luminescent materialis relatively low, possible stability issues with this material haveless influence on the life-time of the phosphor converted LED as awhole, and the phosphor converted LED as a whole is more stable comparedto phosphor converted LEDs which have much more luminescent materialwhich emits light in a relatively narrow spectral distribution in theorange/red spectral range.

In other words, instead of using a single red emitting phosphor, ahybrid solution is applied in the phosphor converted LED of the firstaspect of the invention wherein one of the two luminescent materialsemits enough light at relatively high wavelengths, but prevents theemission of much light in the deep red spectral range and wherein theother luminescent material is used to emit enough light in the whole redspectral range (and possibly the orange spectral range) such that thecolor rendering index is not reduced and the amount of required quantumdots is reduced. It is to be noted that the second and third luminescentmaterial have to be used in the specific combination as disclosed. Ifone of the luminescent materials would not be used and the amount of theother one of the luminescent materials has to be increased and, thus, itwould result in one of the undesired effects of a reduced color rendingindex, a reduced lumen equivalent or a too large use of the thirdluminescent material.

It is to be noted that the term spectral distribution refers to thedistribution of the amount of light at specific wavelengths of light.The amount of light may be expressed as the amount of energy emitted atthe specific wavelength. Such a spectral distribution may also be anormalized distribution. The visible light spectrum may be subdivided inseveral spectral sub ranges in relation to the color which is seen bythe human naked eye. The blue spectral range comprises light with awavelength in the range from 400 nanometer to 500 nanometer. The greenspectral range comprises light with a wavelength in the range from 500nanometer to 570 nanometer. The orange spectral range comprises lightwith a wavelength in the range from 570 nanometer to 620 nanometer. Thered spectral range comprises light with a wavelength in the range from620 nanometer to 750 nanometer. The orange/red spectral range compriseslight in the spectral range from 570 to 750 nanometer.

Optionally, the second and/or the third luminescent material comprises ared emitting Eu²⁺ phosphor.

Optionally, the second luminescent material comprises the materialM₂Si₅N₈:Eu²⁺ (M=alkaline earth metal). (It has been found by theinventors that the phosphors of the material of this optional embodimentis especially useful in the invention as claimed. The specific emissionproperties of the material are set by the combination of alkaline earthatoms and concentration of the Eu activator. The material is configuredto absorb blue light, is stable and provides an advantageous wide lightemission distribution in the orange and red spectral range such that,when being combined with a narrow red emitting luminescent material anda green emitting luminescent material, a phosphor converted LED may bemanufactured with a relatively high Color Rendering Index and arelatively high lumen equivalent.

Optionally, the second luminescent material comprises the material(Ca,Sr)AlSiN₃:Eu²⁺.

Optionally, the third luminescent material comprises particles showingquantum confinement and having at least in one dimension a size in thenanometer range.

Quantum confinement means that the particles have optical propertiesthat depend on the size of the particles. Examples of such materials arequantum dots, quantum rods and quantum tetrapods. The third luminescentmaterial comprises at least particles that have at least in onedimension a size in the nanometer range. This means, for example, that,if the particles are substantially spherical, their diameter is in thenanometer range. Or, this means, for example, if they are wire-shaped,that a size of a cross-section of the wire is in one direction in thenanometer range. A size in the nanometer range means that their size isat least smaller than 1 micrometer, thus, smaller than 500 nanometer,and larger or equal to 0.5 nanometer. In an embodiment, the size in onedimension is smaller than 50 nanometer. In another embodiment the sizein one dimension is in the range from 2 to 30 nanometer.

In embodiments of the invention the third luminescent materials maycomprise quantum dots. Quantum dots are small crystals of semiconductingmaterial generally having a width or diameter of only a few nanometers.When excited by incident light, a quantum dot emits light of a colordetermined by the size and material of the crystal. Light of aparticular color can, therefore, be produced by adapting the size of thedots. Most known quantum dots with emission in the visible range arebased on cadmium selenide (CdSe) with shell such as cadmium sulfide(CdS) and zinc sulfide (ZnS). Cadmium free quantum dots such as indiumphosphide (InP), and copper indium sulfide (CuInS₂) and/or silver indiumsulfide (AgInS₂) can also be used. Quantum dots have a narrow emissionband and, thus, they emit saturated colors. Furthermore, the emissioncolor can easily be tuned by adapting the size of the quantum dots. Anytype of quantum dot known in the art may be used in the presentinvention, provided that it has the appropriate wavelength conversioncharacteristics.

In an optional alternative embodiment, the third luminescent materialcomprises at least one of: a narrow band red emitting phosphor which ishexafluorosilicates activated with Me ions, or a red emitting phosphorCaS:Eu.

Optionally, the third peak wavelength is within the range from 575nanometer to 615 nanometer. In another optional embodiment, the thirdpeak wavelength is within the range from 590 nanometer to 610 nanometer.If the peak wavelength of the third spectral distribution is in one ofthese optional ranges, there are still enough wavelengths available atwhich the third luminescent material may emit light such that enoughlight is emitted at different wavelengths in the red spectral range suchthat a relatively high Color Rendering Index is obtained and such thatthe lumen equivalent of a phosphor converted LED comprising the secondand third luminescent material is high enough.

Optionally, the third spectral width is larger than 80 nanometerexpressed as a Full Width Half Maximum value. If the third spectralwidth is large enough, the second luminescent material emits enoughlight in the orange and the red spectral range such that a high enoughColor Rendering Index is obtained and such that the amount of the thirdluminescent material may be kept relatively low. As discussedpreviously, a relative small amount of the third luminescent materialresults in a phosphor converted LED which is more stable and has alonger life-time.

Optionally, a wavelength difference between the third peak wavelengthand the fourth peak wavelength is at least larger than 10 nanometer. Ifthe difference between the peak wavelengths is large enough, the lightemitted by the second and third luminescent material is spread along awide enough spectral range in order to obtain a high enough ColorRendering Index. As a rule of thumb, the larger the fourth peakwavelength is, the larger the wavelength difference has to be.

Optionally, the fourth peak wavelength is larger than 610 nanometer. Ifthe fourth peak wavelength is high enough, enough light is emitted inthe red spectral range such that the Color Rendering Index remains highenough. If the fourth peak wavelength has a large enough value, there isstill a relatively large portion of the orange/red spectral rangeavailable at which the second luminescent material may have its thirdpeak wavelength.

Optionally, the fourth spectral width is smaller than 60 nanometerexpressed as a Full Width Half Maximum Value. If the fourth spectralwidth is smaller than 60 nanometer, it is prevented that too much lightis emitted in the deep red spectral range in order to prevent areduction of the lumen equivalent of the phosphor converted LED.

Optionally, the power of the light emitted by the fourth luminescentmaterial is less than 20% of the power of all light emitted by thephosphor converted Light Emitting Diode. If the power of the lightemitted by the fourth luminescent material, expressed as a portion ofthe total power emitted by the phosphor converted LED, is low enough,the amount of the fourth material to be used is relatively low and theamount of light emitted in the deep red spectral range is relativelylow. Thus, the phosphor converted LED is more stable and has arelatively high lumen equivalent.

Optionally, the first luminescent material comprises a green emittingphosphor which is one of garnet Y₃Al₅O₁₂:Ce³⁺, (Lu_(0.5),Y_(0.5))₃Al₅O₁₂:Ce³⁺, or Y substituted with Gd or Al substituted withGa, or a SiAlON phosphor. It has been proved that these materials aresuitable for use in the invention to obtain a relatively high ColorRendering Index, a relatively high lumen equivalent, and a relativelystable phosphor converted LED.

Optionally, the first peak wavelength is in the range of 440-460nanometer. Blue emitting Light Emitting Diodes which emit light at thespecified wavelength are relatively cheap and relatively efficient.Additionally, this light is well absorbed by the respective luminescentmaterials of the invention.

According to the second aspect of the invention, a lamp is providedwhich comprises a phosphor converted LED according to the first aspectof the invention. The lamp according to the second aspect of theinvention may be a retro-fit light bulb or a retro-fit light tube. Inother embodiments, the lamp has another shape, for example, the shape ofa box or troffer.

According to the third aspect of the invention, a luminaire is providedwhich comprises a phosphor converted LED according to the first aspectof the invention or which comprises a lamp according to the secondaspect of the invention.

The lamp according to the second aspect of the invention and theluminaire according to the third aspect of the invention provide thesame benefits as the phosphor converted LED according to the firstaspect of the invention and have similar embodiments with similareffects as the corresponding embodiments of the phosphor converted LED.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereinafter.

It will be appreciated by those skilled in the art that two or more ofthe above-mentioned options, implementations, and/or aspects of theinvention may be combined in any way deemed useful.

Modifications and variations of the phosphor converted Light EmittingDiode, the lamp, and/or of the luminaire, which correspond to thedescribed modifications and variations of the phosphor converted LightEmitting Diode, can be carried out by a person skilled in the art on thebasis of the present description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIGS. 1a to 1c schematically present cross-sectional views of differentstructures of phosphor converted Light Emitting diodes according to thefirst aspect of the invention,

FIG. 2a schematically presents a first light emission spectrum of afirst embodiment of a phosphor converted LED,

FIG. 2b schematically presents a second light emission spectrum of asecond embodiment of a phosphor converted LED,

FIG. 3a schematically presents a third light emission spectrum of athird embodiment of a phosphor converted LED,

FIG. 3b schematically presents a fifth light emission spectrum of afourth embodiment of a phosphor converted LED,

FIG. 4a schematically presents a sixth light emission spectrum of afifth embodiment of a phosphor converted LED,

FIG. 4b schematically presents a seventh light emission spectrum of asixth embodiment of a phosphor converted LED,

FIG. 5 schematically presents a seventh light emission spectrum of aseventh embodiment of a phosphor converted LED,

FIGS. 6a to 6c schematically present different embodiments of a lamp,and

FIG. 7 schematically presents an embodiment of a luminaire.

It should be noted that items denoted by the same reference numerals indifferent Figures have the same structural features and the samefunctions, or are the same signals. Where the function and/or structureof such an item have been explained, there is no necessity for repeatedexplanation thereof in the detailed description.

The Figures are purely diagrammatic and not drawn to scale. Particularlyfor clarity, some dimensions are exaggerated strongly.

DETAILED DESCRIPTION

A first embodiment is shown in FIG. 1a . FIG. 1a presents a phosphorconverted Light Emitting Diode (LED) 100. The phosphor converted LightEmitting diode 100 comprises a Light Emitting Diode (LED) 102 and aluminescent element 104. The luminescent element 104 is provideddirectly on top of the LED, more in particular, on top of a surface ofthe LED which emits light.

The LED 102 emits light in a first spectral distribution which has afirst peak wavelength in the blue spectral range. The blue spectralrange comprises light with a wavelength in the range from 445 nanometerto 495 nanometer. The luminescent element 104 comprises a firstluminescent material, a second luminescent material and a thirdluminescent material. The different luminescent materials are providedas a mix in the luminescent element 104. The luminescent element 104receives light emitted by the LED. The first luminescent material isconfigured to absorb a portion of the light of the first spectraldistribution and to convert a portion of the absorbed light towardslight of a second spectral distribution which has a second peakwavelength in the green spectral range. The green spectral rangecomprises light with a wavelength in the range from 495 nanometer to 570nanometer. The second luminescent material is configured to absorb aportion of the light of the first spectral distribution and to convert aportion of the absorbed light towards light of a third spectral rangewhich has a third spectral width and has a third peak wavelength. Thethird luminescent material is configured to absorb a portion of thelight of the first spectral distribution and to convert a portion of theabsorbed light towards light of a fourth spectral range which has afourth spectral width and has a fourth peak wavelength. The third peakwavelength and the fourth peak wavelength are in the orange/red spectralrange, which means that each one of the third and the fourth peakwavelength are in the orange spectral range or in the red spectralrange. The orange spectral range comprises light with a wavelength inthe range from 590 nanometer to 620 nanometer. The red spectral rangecomprises light with a wavelength in the range from 620 nanometer to 750nanometer. Thus, the orange/red spectral range comprises light in thespectral range from 590 to 750 nanometer. Furthermore, the third peakwavelength is smaller than the fourth peak wavelength. Additionally, thethird spectral width is larger than the fourth spectral width. It is tobe noted that the luminescent element 104 may be based on a matrixpolymer, such as for example, Polymethyl methacrylate (PMMA),Polyethylene terephthalate (PET), Polyethylene naphthalate (PEN) orpolycarbonate (PC). Particles and/or molecules of the first luminescentmaterial, the second luminescent material and the third luminescentmaterial may be dispersed and/or dissolved in the matrix polymer. Inother embodiments, the luminescent element 104 may be an ceramic element104 when inorganic luminescent materials are used.

FIG. 1b schematically present an alternative structure of a phosphorconverted LED 130. The phosphor converted LED 130 is similar to thephosphor converted LED 100 of FIG. 1a , however, a difference is thatthe luminescent element 104 is not directly arranged on top of the LED102, but a gap 132 is present between the LED 102 and the luminescentelement 104. The gap may have a depth of, for example, 500 micrometer,but may also have a depth of a few millimeter.

FIG. 1c schematically presents another alternative structure of aphosphor converted LED 160. The phosphor converted LED 160 is similar tothe phosphor converted LED 100 of FIG. 1a , however, a difference isthat phosphor converted LED 160 does not have the luminescent element104 of FIG. 1a , but has a stack of luminescent layers which is arrangedon top of a light emitting surface of the LED 102. The stack ofluminescent layers comprises a first layer 166 with one of the first,the second, or the third luminescent materials. The first layer 166 isprovided directly on the light emitting surface of the LED 102. Thestack further comprises a second layer 164 which is interposed betweenthe first layer 166 and a third layer 162. The second layer 164comprises another one of the first, the second or the third luminescentmaterial. The third layer 162 comprises a further luminescent materialof the group of the first, the second and the third luminescentmaterials. In other words, in each one of the first, the second and thethird layer, is arranged one of the luminescent materials of the groupof the first, the second and the third luminescent materials. Each oneof the layers may be based on a matrix polymer in which the respectiveluminescent material is dispersed or dissolved. Each one of the layersmay also be a ceramic layer if the respective luminescent material is aninorganic compound. It is further to be noted that, in FIG. 1c , thestack of luminescent layers is provided on top of the LED 102, however,in an alternative embodiment, there is a gap present between the LED 102and stack of luminescent layers.

In the following, different embodiments of phosphor converted LEDs arediscussed. It is to be noted that in the following embodiment are mainlyrelated to the specific luminescent materials used in the phosphorconverted LEDs. The phosphor converted LEDs of the following embodimentsmay have the structure of one of the above discussed embodiments of thestructure of the phosphor converted LEDs.

Embodiment 1

The phosphor converted LED of embodiment 1 comprises a blue lightemitting LED which emits a first spectral distribution with a peakwavelength of 449 nanometer. A green emitting phosphor with the formulaY₃Al₅O₁₂:Ce3+ is used as a first luminescent material. The secondluminescent material is a red emitting phosphor from the BSSNE 2-5-8system. The second luminescent material emits light in a light emissiondistribution with a peak wavelength of 597 nanometer and with a spectralwidth of 91 nanometer, expressed as a Full Width Half Maximum value(FWHM). A phosphor from the BSSNE 2-5-8 system has a general formula ofM₂Si₅Ne₈:Eu²⁺ (M=60% Ba, 36% Sr, 3% Ca) with 1% Eu. The thirdluminescent material comprises Quantum Dots which emit according to aspectral distribution which has a peak wavelength of 612 nanometer andwhich has a spectral width of 30 nm (FWHM).

The mixture of luminescent materials is chosen such that the emittedlight by the phosphor converted LED has a correlated color temperature(CCT) of 3000 Kelvin. Such a phosphor converted LED has a light emissiondistribution which is presented in FIG. 2a . The x-axis of the chartrepresents the wavelength of the light and the y-axis the (normalized)intensity of the respective wavelengths. Further, it is known that thephosphor converted LED according to this embodiment has a ColorRendering Index (CRI) of 82.2 (which is expressed as an Ra value). TheLumen Equivalent of this phosphor converted LED is 355.3 lm/W and thelight power emitted by the phosphor converted LED originates for 12.9%directly from the LED, for 61.0% from the first luminescent material(green), for 8.6% from the second luminescent material (orange/redemitting BSSNE phosphor) and for 17.5% from the quantum dots.

When this embodiment is compared to the second embodiment discussed inthe background of the art section (phosphor converted LED with quantumdots), especially the amount of Quantum Dots is significantly reduced.The red emitting quantum dots are not stable enough and by reducingtheir required amount, the total stability of the phosphor converted LEDincreases. Also, possible environmental issues of Quantum Dots arereduced (when the Quantum Dots comprise, for example, Cadmium orSelenium).

Embodiment 2

The phosphor converted LED of embodiment 2 comprises a blue lightemitting LED which emits a first spectral distribution with a peakwavelength of 449 nanometer. A green emitting phosphor with the formulaY₃Al₅O₁₂:Ce³⁺ is used as a first luminescent material. The secondluminescent material is a red emitting phosphor from the BSSNE 2-5-8system. The second luminescent material emits light in a light emissiondistribution with a peak wavelength of 605 nanometer and with a spectralwidth of 96 nanometer FWHM. The third luminescent material comprisesQuantum Dots with emit according to a spectral distribution which has apeak wavelength of 612 nanometer and which has a spectral width of 30 nm(FWHM).

The mixture of luminescent materials is chosen such that the emittedlight by the phosphor converted LED has a correlated color temperature(CCT) of 3000 Kelvin. Such a phosphor converted LED has a light emissiondistribution which is presented in FIG. 2b . Further, it is known thatthe phosphor converted LED according to this embodiment has a ColorRendering Index (CRI) of 81.8 (which is expressed as the Ra value). TheLumen Equivalent of this phosphor converted LED is 340 lm/W and thelight power emitted by the phosphor converted LED originates for 11.9%directly from the LED, for 46.7% from the first luminescent material(green), for 33.3% from the second luminescent material (orange/redemitting BSSNE phosphor) and for 8.2% from the quantum dots.

Embodiment 3

The phosphor converted LED of embodiment 3 comprises a blue lightemitting LED which emits a first spectral distribution with a peakwavelength of 449 nanometer. A green emitting phosphor with the formulaY₃Al₅O₁₂:Ce³⁺ is used as a first luminescent material. The secondluminescent material is a red emitting phosphor from the BSSNE 2-5-8system. The second luminescent material emits light in a light emissiondistribution with a peak wavelength of 580 nanometer and with a spectralwidth of 90.3 nanometer FWHM. The third luminescent material comprisesQuantum Dots which emit according to a spectral distribution which has apeak wavelength of 630 nanometer and which has a spectral width of 25 nm(FWHM).

The mixture of luminescent materials is chosen such that the emittedlight by the phosphor converted LED has a correlated color temperature(CCT) of 3000 Kelvin. Such a phosphor converted LED has a light emissiondistribution which is presented in FIG. 3a . Further, it is known thatthe phosphor converted LED according to this embodiment has a ColorRendering Index (CRI) of 81.6 (which is expressed as the Ra value).

Embodiment 4

In a first comparative example, in the context of embodiment 4 of theinvention, a first comparative phosphor converted LED is discussed whichdoes not have the third luminescent material. This first comparativephosphor converted LED comprises a blue light emitting LED which emits aspectral distribution with a peak wavelength of 449 nanometer. A greenemitting phosphor with the formula (Lu_(0.5), Y_(0.5))₃Al₅O₁₂:Ce³⁺ isused as a luminescent material. A red emitting (Sr,Ca)AlSiN₃Eu²⁺activated phosphor with a peak emission at 635 nanometer and a spectralwidth of 101 nanometer FWHM is used in the first comparative phosphorconverted LED. The mixture of luminescent materials is chosen such thatthe emitted light by the first comparative phosphor converted LED has acorrelated color temperature (CCT) of 2700 Kelvin. Further, it is knownthat the first comparative phosphor converted LED according to thisembodiment has a Color Rendering Index (CRI) of 90.2 (which is expressedas the RA value). The Lumen Equivalent of this phosphor converted LED is278 lm/W and the light power emitted by the phosphor converted LEDoriginates for 7.8% directly from the LED, for 40.0% from the greenemitting phosphor and for 52.3% from the red emitting phosphor.

In a second comparative example, in the context of embodiment 4 of theinvention, a second comparative phosphor converted LED is discussedwhich does not have the second luminescent material. This secondcomparative phosphor converted LED comprises a blue light emitting LEDwhich emits a spectral distribution with a peak wavelength of 449nanometer. A green emitting phosphor with the formula (Lu_(0.5),Y_(0.5))₃Al₅O₁₂:Ce³⁺ is used as a luminescent material. Red emittingQuantum Dots, which have a peak emission at 620 nanometer and a spectralwidth of 25 nanometer FWHM, are used in the second comparative phosphorconverted LED. The mixture of luminescent materials is chosen such thatthe emitted light by the second comparative phosphor converted LED has acorrelated color temperature (CCT) of 2700 Kelvin. Further, it is knownthat the second comparative phosphor converted LED according to thisembodiment has a Color Rendering Index (CRI) of 90.2 (which is expressedas the Ra value). The Lumen Equivalent of this phosphor converted LED is350 lm/W and the light power emitted by the phosphor converted LEDoriginates for 9.4% directly from the LED, for 56.1% from the greenemitting phosphor and for 34.4% from the red emitting phosphor.

The phosphor converted LED of embodiment 4 of the first aspect of theinvention comprises a blue light emitting LED which emits a firstspectral distribution with a peak wavelength of 449 nanometer. A greenemitting phosphor with the formula (Lu_(0.5), Y_(0.5))₃Al₅O₁₂:Ce³⁺ isbeing used as a first luminescent material. The second luminescentmaterial is a red emitting phosphor which has a light emissiondistribution with a peak wavelength of 580 nanometer and with a spectralwidth of 91 nanometer FWHM. The second luminescent material comprisesM₂Si₅N₈:Eu²⁺ (M=90% Ba, 10% Sr) phosphor with 0.4% Eu. The thirdluminescent material comprises Quantum Dots which emit according to aspectral distribution which has a peak wavelength of 630 nanometer andwhich has a spectral width of 25 nm (FWHM).

The mixture of luminescent materials is chosen such that the emittedlight by the phosphor converted LED has a correlated color temperature(CCT) of 2700 Kelvin. Such a phosphor converted LED has a light emissiondistribution which is presented in FIG. 3b . Further, it is known thatthe phosphor converted LED according to this embodiment has a ColorRendering Index (CRI) of 90.5 (which is expressed as the Ra value). TheLumen Equivalent of this phosphor converted LED is 336 lm/W and thelight power emitted by the phosphor converted LED originates for 9.3%directly from the LED, for 41.1% from the first luminescent material(green), for 23.4% from the second luminescent material (orange/redemitting phosphor) and for 26.2% from the quantum dots.

When the phosphor converted LED is compared to the first comparativephosphor converted LED, it is seen that the lumen equivalent issubstantially higher. When the phosphor converted LED is compared to thesecond comparative phosphor converted LED, it is seen that the ColorRendering Index has about the same value, that the lumen equivalent isat about the same level, and that the contribution of the quantum dotsto the light emission is relatively low, and, thus, that the amount ofquantum dots in the phosphor converted LED of embodiment 4 issignificantly lower than the amount of quantum dots in the secondcomparative example.

Embodiment 5

The fifth embodiment of a phosphor converted LED is being simulated in asoftware program in order to get in insight in the use of a specificnarrow band emitting red phosphor which is being disclosed in patentapplication US2006/0169998. In US2006/0169998 it has been disclosed thathexafluorosilicates activated with Mn4+ ions show a narrow red emissionat about 630 nm peak.

The phosphor converted LED of embodiment 5 comprises a blue lightemitting LED which emits a first spectral distribution with a peakwavelength of 449 nanometer. A green emitting phosphor with the formulaY₃Al₅O₁₂:Ce³⁺ is used as a first luminescent material. The secondluminescent material is a red emitting phosphor with a peak wavelengthof 590 nanometer and with a spectral width of 87 nanometer FWHM. Thesecond luminescent material comprises M₂Si₅N₈:Eu²⁺ (M=60% Ba, 40% Sr)with 0.4% Eu. The third luminescent material comprises K₂SiF₆:Mn asdescribed in US2006/0169998 (which has a narrow band light emission inthe red spectral range).

The mixture of luminescent materials is chosen such that the emittedlight by the phosphor converted LED has a correlated color temperature(CCT) of 2700 Kelvin. Such a phosphor converted LED has a light emissiondistribution which is presented in FIG. 4a . Further, it is known thatthe phosphor converted LED according to this embodiment has a ColorRendering Index (CRI) of 90.7 (which is expressed as the Ra value). TheLumen Equivalent of this phosphor converted LED is 344 lm/W and thelight power emitted by the phosphor converted LED originates for 9.5%directly from the LED, for 45.5% from the first luminescent material(green), for 19.9% from the second red emitting luminescent material andfor 25.1% from the phosphor K₂SiF₆:Mn.

Embodiment 6

The sixth embodiment of a phosphor converted LED is being simulated inorder to get an insight in the use of a specific narrow band emittingred phosphor which is being disclosed in patent applicationUS2006/0169998. In US2006/0169998 it has been disclosed thathexafluorosilicates activated with Mn4+ ions show a narrow red emissionat about 630 nm peak.

The phosphor converted LED of embodiment 6 comprises a blue lightemitting LED which emits a first spectral distribution with a peakwavelength of 449 nanometer. A green emitting phosphor with the formulaY₃Al₅O₁₂:Ce³⁺ is used as a first luminescent material. The secondluminescent material is a red emitting phosphor with a peak wavelengthof 600 nanometer and with a spectral width of 87 nanometer FWHM. Thesecond luminescent material comprises M₂Si₅N₈:Eu²⁺ (M=50% Ba, 50% Sr)with 1% Eu. The third luminescent material comprises K₂SiF₆:Mn asdescribed in US2006/0169998 (which has a narrow band light emission inthe red spectral range). Compared to Embodiment 6, the amount of thethird luminescent material is reduced.

The mixture of luminescent materials is chosen such that the emittedlight by the phosphor converted LED has a correlated color temperature(CCT) of 2700 Kelvin. Such a phosphor converted LED has a light emissiondistribution which is presented in FIG. 4b . Further, it is known thatthe phosphor converted LED according to this embodiment has a ColorRendering Index (CRI) of 81.5 (which is expressed as the Ra value). TheLumen Equivalent of this phosphor converted LED is 346 lm/W and thelight power emitted by the phosphor converted LED originates for 9.6%directly from the LED, for 41.6% from the first luminescent material(green), for 36.3% from the second red emitting luminescent material andfor 12.5% from the phosphor K₂SiF₆:Mn.

Embodiment 7

The phosphor converted LED of embodiment 7 comprises a blue lightemitting LED which emits a first spectral distribution with a peakwavelength of 449 nanometer. A green emitting phosphor with the formula(Lu_(0.5), Y_(0.5))₃Al₅O₁₂:Ce³⁺ is being used as a first luminescentmaterial. The second luminescent material is a red emitting phosphorwith a peak wavelength of 612 nanometer and with a spectral width of 87nanometer FWHM. The second luminescent material comprises M₂Si₅N₈:Eu²⁺(M=50% Ba, 50% Sr) with 3% Eu. The third luminescent material comprisesCaS:Eu which has a light emission distribution with a peak wavelength at650 nanometer and a spectral width of 66 nm FWHM.

The mixture of luminescent materials is chosen such that the emittedlight by the phosphor converted LED has a correlated color temperature(CCT) of 2700 Kelvin. Such a phosphor converted LED has a light emissiondistribution which is presented in FIG. 5. Further, it is known that thephosphor converted LED according to this embodiment has a ColorRendering Index (CRI) of 84.6 (which is expressed as the Ra value). TheLumen Equivalent of this phosphor converted LED is 313 lm/W and thelight power emitted by the phosphor converted LED originates for 10.7%directly from the LED, for 45.8% from the first luminescent material(green), for 30.0% from the second red emitting luminescent material andfor 13.5% from the phosphor CaS:Eu.

On basis of the discussed embodiments of a phosphor converted LED onemay conclude that by combining a broadband emitting red phosphor with anarrow band red light emitting luminescent material in a phosphorconverted LED which has a blue emitting LED and a green phosphor, aphosphor converted LED may be obtained which has a relatively high ColorRendering Index, have a relatively high lumen equivalent, and have arelatively long life time because of the use of a relatively low amountof narrowband red emitting luminescent materials.

FIG. 6a schematically shows a first embodiment of a lamp in accordancewith the second aspect of the invention. The lamp is a retrofitlight-tube 600. The light-tube 600 comprises, in a lateral direction, aplurality of phosphor converted LEDs 602. The glass of the light-tube600 is the light exit window and the phosphor converted LEDs 602 emitlight towards the light exit window.

FIG. 6b schematically shows a second embodiment of a lamp which is aretrofit light bulb 630. The retrofit light bulb 630 comprises a base onwhich, at least one, phosphor converted LED 632 in accordance with thefirst aspect of the invention is provided.

FIG. 6c schematically shows a third embodiment of a lamp which is a LEDunit 660. The LED unit 660 comprises a housing 664 which has acylindrical shape. The housing 664 encloses a cavity in which aplurality of phosphor converted LEDs 666 according to the first aspectof the invention are provided. The light exit window is formed by alayer 662 which closes the cavity. The layer 662 may be a diffusinglayer. Alternatively, the layer 662 may be a transparent layer.

FIG. 7 schematically shows a luminaire 700 according to the third aspectof the invention. The luminaire comprises one or more light emittingassemblies according to the first aspect of the invention or comprises alamp according to the second aspect of the inventions.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. Use of the verb “comprise” and itsconjugations does not exclude the presence of elements or steps otherthan those stated in a claim. The article “a” or “an” preceding anelement does not exclude the presence of a plurality of such elements.The invention may be implemented by means of hardware comprising severaldistinct elements. In the device claim enumerating several means,several of these means may be embodied by one and the same item ofhardware. The mere fact that certain measures are recited in mutuallydifferent dependent claims does not indicate that a combination of thesemeasures cannot be used to advantage.

1. A device comprising: a light source emitting a first spectraldistribution having a first peak wavelength in the blue spectral range,a first luminescent material configured for absorbing a portion of thelight of the first spectral distribution and for converting at least aportion of the absorbed light into light of a second spectraldistribution, the second spectral distribution having a second peakwavelength in the green spectral range, a second luminescent materialconfigured for absorbing a portion of the light of the first spectraldistribution and/or a portion of the second spectral distribution andfor converting at least a portion of the absorbed light into light of athird spectral distribution, the third spectral distribution having athird spectral width and having a third peak wavelength, a thirdluminescent material configured for absorbing a portion of the light ofat least one of the first spectral distribution, second spectraldistribution, and the third spectral distribution and for converting atleast a portion of the absorbed light into light of a fourth spectraldistribution, the fourth spectral distribution having a fourth spectralwidth and having a fourth peak wavelength, wherein the third peakwavelength and the fourth peak wavelength are in the orange/red spectralrange, and wherein the third luminescent material comprises particlesshowing quantum confinement and having at least in one dimension a sizein the nanometer range.
 2. The device of claim 1 wherein the third peakwavelength is smaller than the fourth peak wavelength, and the thirdspectral width is larger than the fourth spectral width.
 3. The deviceof claim 1 wherein the second luminescent material comprises one of ared emitting Eu²⁺ phosphor, M₂Si₅N₈:Eu²⁺ where M is an alkaline earthmetal, and (Ca,Sr)AlSiN₃:Eu²⁺.
 4. The device of claim 1 wherein thefirst luminescent material, second luminescent material, and thirdluminescent material are mixed in a single layer.
 5. The device of claim4 further comprising a gap disposed between the light source and thesingle layer.
 6. The device of claim 4 wherein the single layer is aceramic.
 7. The device of claim 1 wherein particles of the firstluminescent material, second luminescent material, and third luminescentmaterial are dispersed and/or dissolved in a matrix polymer.
 8. Thedevice of claim 7 wherein the matrix polymer is one of polymethylmethacrylate, polyethylene terephthalate, polyethylene naphthalate, andpolycarbonate.
 9. The device of claim 1 wherein the first luminescentmaterial, the second luminescent material, and the third luminescentmaterial are stacked on the light source.
 10. The device of claim 9wherein one of the first luminescent material, the second luminescentmaterial, and the third luminescent material is dispersed in a matrixpolymer.
 11. The device of claim 9 wherein one of first luminescentmaterial, the second luminescent material, and the third luminescentmaterial is disposed in a ceramic layer.
 12. The device of claim 1,wherein the third spectral width is larger than 80 nanometers expressedas a Full Width Half Maximum value, and the fourth spectral width isless than 60 nanometers expressed as a Full Width Half Maximum value.13. The device of claim 1, wherein a wavelength difference between thethird peak wavelength and the fourth peak wavelength is greater than 10nanometers.
 14. The device of claim 1, wherein a power of light emittedby the third luminescent material is less than 20% of a power of alllight emitted by the device.
 15. The device of claim 1, wherein thefirst luminescent material comprises a green emitting phosphor which isone of garnet Y₃Al₅O₁₂:Ce³⁺, a SiAlON phosphor or(Lu_(0.5),Y_(0.5))₃Al₅O₁₂:Ce³⁺. or Y substituted with Gd or Alsubstituted with Ga, or a mixture of garnets.